1. Field of the Invention
The present invention relates to a hydraulic braking pressure control system comprising auxiliary hydraulic pressure generating means connected to a brake device for generating a hydraulic pressure depending upon a braking operation by a brake pedal; a hydraulic pressure supply source; hydraulic pressure supply source hydraulic pressure control means capable of controlling the hydraulic pressure from the hydraulic pressure supply source in accordance with the braking operation by the brake pedal; hydraulic pressure transmitting means which is interposed in a hydraulic pressure path extending from the hydraulic pressure supply source via the hydraulic pressure supply source hydraulic pressure control means to the brake device and which is arranged to permit the transmission of the hydraulic pressure output from the hydraulic pressure supply source hydraulic pressure control means to the brake device when the hydraulic pressure in the hydraulic pressure supply source is normal and to cut off the flowing of a working fluid from the brake device toward the hydraulic pressure supply source when the hyrdraulic pressure in the hydraulic pressure supply source is abnormally reduced; and an on-off value interposed between the auxiliary hydraulic pressure generating means and the brake device, having a pilot chamber leading to an output port of the hydraulic pressure supply source hydraulic pressure control means, and adapted to be closed in response to an increase in hydraulic pressure in the pilot chamber.
2. Description of the Prior Art
Such hydraulic braking pressure control system is conventionally known, for example, from Japanese Patent Publication No. 53263/86 and the like.
Such hydraulic braking pressure control system is constructed such that during a normal braking wherein the hydraulic pressure supply source is normal, the on-off valve is closed by the hydraulic pressure from the hydraulic pressure supply source hydraulic pressure control means, so that the hydraulic pressure from the hydraulic pressure supply source hydraulic pressure control means is applied to the brake device, while when the hydraulic pressure supply source is in failure, the hydraulic braking pressure is applied from the auxiliary hydraulic pressure generating means to the brake device in response to the opening of the on-off valve due to the reduction of the hydraulic pressure in the hydraulic pressure supply source. During a braking operation by the brake pedal, the hydraulic pressure is delivery from both of the auxiliary hydraulic pressure generating means and the hydraulic pressure supply source hydraulic pressure control means, and when the hydraulic pressure supply source is normal, the on-off valve should be closed by the hydraulic pressure control means before the hydraulic pressure from the auxiliary hydraulic pressure generating means is applied to the brake device. If not so, the operation of the brake device is not smooth.
In the above hydraulic braking pressure control system, if the hydraulic pressure from the hydraulic pressure supply source hydraulic pressure control means is applied to the brake device through the hydraulic pressure transmitting means before the on-off valve is closed by the output hydraulic pressure from the hydraulic pressure supply source hydraulic pressure control means is an initial stage of the braking operation by the brake pedal, the hydraulic braking pressure is applied to the brake device from both of the auxiliary hydraulic pressure generating means and the hydraulic pressure supply source hydraulic pressure control means before closing of the on-off valve. Therefore, it is necessary to apply the hydraulic pressure output from the hydraulic pressure supply source hydraulic pressure control means to the hydraulic pressure transmitting means after closing of the on-off valve.
Further, when the hydraulic pressure from the hydraulic pressure supply source hydraulic pressure control means and the hydraulic pressure from the auxiliary hydraulic pressure generating means are applied in a switched manner to the brake device, it is required that such switching is conducted concurrently in a plurality of brake devices.